This invention relates to drag reduction on submersible or submerged objects, and more specifically to submersible objects having a drag reduction coating of hydrophobic silica. A factor which limits speed and increases fuel consumption of surface and subsurface vessels is the drag resistance effected at the interface of the vessel with the aqueous environment. In recent years, serious attempts have been made to reduce the friction coefficient between seagoing vessels and the medium in which they travel by the introduction of long chain hydrophilic polymers into the vicinity of the interface between the hull of the vessel and the water. Typical hydrophilic polymers are:
A. Polyethylene oxide, in molecular weight of 1 to 5 million.
B. Natural products such as okra.
C. High molecular weight derivatives of substituted polyethyleneimines.
The inherent disadvantages of these materials, however, are that they require a continuous flow of the material over the vessel during motion and imply the use of pumping equipment, metering devices, and the associated weight of this equipment and materials in areas which are normally confined. The use of this approach offers no particular advantage to a vessel at rest and would require anchoring devices as cumbersome as those in current use. Additionally the material is dispersed in the water resulting in an undesirable ecological effect. Thus, the advantages of currently used drag reducing equipment do not outweigh the disadvantages.
Various coatings are also used to reduce drag. Hydrophilic acrylic resins are known as drag reducing coatings. Polybutadiene and polyurethane coatings are also drag reducing coatings. These materials are adequate, but there is still room for improvement. The drag reducing coatings of the present invention provide improved drag reducing coatings which are useful for ship's hull of surface and subsurface ships, and other devices which move through or under water.